Various hybrid powertrain architectures are known for managing the input and output torques of various prime-movers in hybrid vehicles, most commonly internal combustion engines and electric machines. Series hybrid architectures are generally characterized by an internal combustion engine driving an electric generator which in turn provides electrical power to an electric drivetrain and to a battery pack. The internal combustion engine in a series hybrid is not directly mechanically coupled to the drivetrain. The electric generator may also operate in a motoring mode to provide a starting function to the internal combustion engine, and the electric drivetrain may recapture vehicle braking energy by also operating in a generator mode to recharge the battery pack. Parallel hybrid architectures are generally characterized by an internal combustion engine and an electric motor which both have a direct mechanical coupling to the drivetrain. The drivetrain conventionally includes a shifting transmission to provide the necessary gear ratios for wide range operation.
Electrically variable transmissions (EVT) are known which provide for continuously variable speed ratios by combining features from both series and parallel hybrid powertrain architectures. EVTs are operable with a direct mechanical path between an internal combustion engine and a final drive unit thus enabling high transmission efficiency and application of lower cost and less massive motor hardware. EVTs are also operable with engine operation mechanically independent from the final drive or in various mechanical/electrical split contributions thereby enabling high-torque continuously variable speed ratios, electrically dominated launches, regenerative braking, engine off idling, and multi-mode operation.
An EVT control relies upon an engine operable in a torque control mode to provide an input torque in accordance with predetermined engine torque operating points commanded by the EVT control. The EVT control includes a system dynamic model which assumes a system torque balance among various controlled and uncontrolled, internal and external torques. Input and output torques are treated by the model as uncontrolled external torques and motor torques are treated by the model as controlled torques. Motor torques are controlled in accordance with the model to control engine speed at the commanded engine torque to a desired engine speed.
Loss of proper operation of one of the motors in such a transmission may make such a control, which relies upon predictable torque production at both motors, impractical for controlling engine speed as intended. Therefore, what is needed is a robust recovery control for the situation where one of the two motors is rendered functionally inoperative so that the vehicle is not stranded due to such a single point system anomaly.